Mechanism Analysis Of Impact Of Rainfall On Traffic State Of Urban Road Network

Urban road traffic operation is influenced by many factors,among which rainfall is a common and important natural factor.People generally feel that urban roads are more prone to traffic congestion under rainfall weather.However,how to quantify the impact of rainfall on urban road traffic state,what is the impact mechanism behind the phenomenon,and how traffic managers can predict the changes of road network traffic state under rainfall conditions need further research.This paper attempts to sort out the underlying logic of traffic congestion under rainfall weather from a theoretical perspective,constructs a model of urban road traffic flow considering the influence of rainfall,and calibrates and validates the model through real data to quantify the nonlinear influence of rainfall on traffic state through the model.This study provides theoretical support for urban traffic refinement management and improves urban traffic operation efficiency,which has important practical significance and value.The main work of the paper is as follows:(1)To verify the differences of urban road traffic flow characteristics under different rainfall levels by using license plate recognition data.Firstly,based on the license plate recognition data,we calculate the flow and travel speed,divide the rainfall level according to the hourly rainfall,and categorize the data according to the rainfall level.On this basis,the average travel speed and road network capacity under different rainfall levels are calculated and compared,and the results show that both gradually decrease with the increase of rainfall level,confirming the adverse effect of rainfall on urban road traffic state.(2)The impact mechanism of rainfall on urban traffic state is revealed through analysis,and the urban road traffic flow model considering rainfall is established and analyzed.Drivers tend to drive conservatively in rainy days,which leads to the increase of headway,the decrease of capacity,and the decrease of free flow speed,and finally the decrease of travel speed.Based on this assertion,the traffic elements are selected and the urban road traffic flow model is constructed.The model shows that the increase of saturation headway is the main cause of the impact of rainfall on traffic state,which causes the road state change from nearsaturated state under non-rainfall conditions to oversaturated under rainfall conditions at the same flow,greatly increasing intersection delays;while the impact on the oversaturated road is small,and almost no impact on the less saturated road.(3)The model is calibrated using the observed data,and the validity and reliability of the model are verified.The saturation headway is obtained from the video capture data,and the free flow speed is estimated from the license plate recognition data using a Gaussian mixture model,and the relationship between the rainfall level and saturation headway and free flow speed is obtained statistically.Plug into the model for numerical simulation to quantify the impact of rainfall on the urban road network traffic state.The traffic operation state under different scenarios is simulated using the road network simulation experiments,and the simulation results are consistent with the numerical calculation results,indicating that the model is valid and reliable.Finally,the traffic management ideas under the rainfall scenario are given.